Generally, gas turbine engines typically include a fan delivering air into a bypass duct defined within a nacelle. Air is also delivered into the engine core. The air flowing through the engine core passes through a compressor section. The air then passes into a combustion section. In the combustion section the air is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors.
It is known to provide a nacelle anti-icing system in the gas turbine engine. The nacelle anti-icing system typically will tap hot air from the compressor section. The hot air is selectively delivered to the lip of the nacelle to provide anti-icing at the lip of the nacelle. This anti-icing function is performed selectively and is not necessary during much of the operation of a gas turbine engine on an aircraft. However, when conditions indicate that there may be icing at the lip of the nacelle, a valve may be opened to deliver the hot air to that location.
An anti-icing system may use a series two-valve configuration to improve the dispatch rate for the aircraft. While both valves are capable of shut off and regulation independently, typically, there is a primary valve that performs the regulation all the time (with a lower regulating set point) and both valves perform the shut off function alternatively. Should the primary valve become incapable of regulating, the operator will lock the primary valve open, and thus enable the secondary valve to regulate. However, since the secondary valve has a higher pressure regulating set point for system stability reasons, the flow will be higher which drives excessive bleed extraction from the engine core flow, increasing both fuel consumption as well as driving the nacelle inlet lip skin higher than it needs to be. It is therefore desirable to have a system that is both stable and has the same flow in both the normal and back up modes. Two mechanical pressure regulating valves with the same setpoint in series would become inherently unstable, especially with the upper valve sensing regulated pressure between the two valves.